Unless otherwise indicated herein, the materials described in this section are not prior art to the claims in this application and are not admitted to be prior art by inclusion in this section.
Flash memory may use a threshold voltage of the memory cell (e.g., an analog quantity) to store digital data by dividing the available range of the threshold voltage into different levels. For example, the threshold voltage for a single-level cell flash memory may be divided into two levels. The threshold voltage for a multi-level cell may be divided into multiple levels (e.g., four levels, or into eight levels for triple-level flash memory). In these examples, the thresholds may be hardwired thresholds that may be assigned to define the boundaries between levels.
To read a value of a memory cell, multiple sensing operations may typically be used. For example, a read voltage may be applied to a control gate of the flash memory cell. A sense amplifier may then be used to determine if the memory cell is conducting at a particular cell threshold voltage. The sensing operations may determine and assign a digital value for each cell based on whether the cell threshold voltage is below the level threshold (conducting) or above the level threshold (cell not conducting). In some cases, the thresholds may be more adaptive with the option for multiple reads using a read-retry feature. A read retry method might be used to obtain the actual threshold voltage. Determining the actual threshold voltage, however, may take a long time.